Refrigerating and air-conditioning system and system controller

ABSTRACT

A refrigerating and air-conditioning system includes a plurality of independent refrigerating and air-conditioning apparatuses each including a refrigerant circuit and a defrosting unit, and further includes a system controller managing the apparatuses in an integrative manner. The system controller includes a defrosting operation control unit. When a time interval between an estimated defrosting start time calculated for a given refrigerating and air-conditioning apparatus and a subsequent estimated defrosting start time calculated for another refrigerating and air-conditioning apparatus is less than or equal to a predetermined target start time interval, the defrosting operation control unit transmits a defrosting start instruction signal to the defrosting unit of the given refrigerating and air-conditioning apparatus.

TECHNICAL FIELD

The present invention relates to a refrigerating and air-conditioning system which includes a plurality of refrigerating and air-conditioning apparatuses and a system controller, and also performs a defrosting operation, the refrigerating and air-conditioning apparatuses being provided to cool the same target space to be cooled, the system controller being provided to manage the refrigerating and air-conditioning apparatuses in an integrative manner.

BACKGROUND ART

As described in Patent Literature 1, a related-art refrigerating and air-conditioning system includes a plurality of independent refrigerating and air-conditioning apparatuses each including a refrigerant cycle. Each of the refrigerating and air-conditioning apparatuses includes a frost detection unit and an indoor coil temperature detecting unit. The system controls the refrigerating and air-conditioning apparatuses such that while one of the refrigerating and air-conditioning apparatuses is performing the defrosting operation or until an indoor coil temperature of the refrigerating and air-conditioning apparatus reaches a predetermined temperature after the defrosting operation is ended, the other refrigerating and air-conditioning apparatuses are not allowed to perform the defrosting operation. Then, the other refrigerating and air-conditioning apparatuses are successively controlled to perform the defrosting operation.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Utility Model Registration Application Publication No. Sho 62-141137 (for example, pages 4-10, FIG. 2)

SUMMARY OF INVENTION Technical Problem

In the above related-art refrigerating and air-conditioning system, when the refrigerating and air-conditioning apparatuses simultaneously satisfy the requirement for starting of the defrosting operation, one of the refrigerating and air-conditioning apparatuses performs the defrosting operation and the other refrigerating and air-conditioning apparatuses are not allowed to perform the defrosting operation. Thus, a cooling capacity of the entire system may greatly drop.

Also, in some systems, in order to solve the problem of the above system, the other refrigerating and air-conditioning apparatuses are allowed to continue performing the cooling operation. In such a system, a so-called “liquid back phenomenon” may occurs as another problem. In this phenomenon, an evaporator on which much frost is formed fails to completely evaporate refrigerant because its cooling capacity is reduced by the frost, and refrigerant being in a two-phase gas-liquid state returns to a compressor, and suddenly expands in the compression chamber, thus causing a failure therein.

Furthermore, a schedule operation system is also present which specifies a defrost start time for each of the refrigerating and air-conditioning apparatuses. However, it is hard for this system also to start defrosting at an optimum timing with respect to the amount of frost which varies in accordance with an indoor environment, etc. The system thus has a problem in energy saving.

The present invention has been made to solve the above problems, and an object of the invention is to provide a refrigerating and air-conditioning system which can simultaneously satisfy the three following requirements: reliability is ensured; a sufficient cooling capacity is maintained; and energy saving characteristics are ensured by maintaining optimum defrosting intervals.

Solution to Problem

In order to attain the above object, a refrigerating and air-conditioning system according to an embodiment of the present invention includes a plurality of independent refrigerating and air-conditioning apparatuses each including a refrigerant circuit in which a compressor, a condenser, an expansion valve and an evaporator are connected, an operation-state detection unit which detects an operation state of the refrigerant circuit, a frost detection unit which detects frost forming on a refrigerant tube for the evaporator, a defrosting unit which removes frost forming on the evaporator, and a controller which controls an operation of the refrigerant circuit. The system further includes a system controller which is connected to the controllers of the plurality of refrigerating and air-conditioning apparatuses such that it can communicate with the controller. The system controller manages operations of the plurality of refrigerating and air-conditioning apparatuses in an integrative manner. The evaporators of the plurality of refrigerating and air-conditioning apparatuses are arranged in a single space to be cooled. The system controller includes an estimated defrosting start-time calculating unit which calculates an estimated defrosting start time, at which a defrosting operation of the defrosting unit will be started, for each of the refrigerating and air-conditioning apparatuses based on the operation state of the above each refrigerating and air-conditioning apparatus, which is detected by the operation-state detection unit, and further includes a defrosting operation control unit which controls, based on the defrosting start time calculated by the estimated defrosting start-time calculating unit, the defrosting operation of the defrosting unit. When a time interval between an estimated defrosting start time calculated for a given refrigerating and air-conditioning apparatus and a subsequent estimated defrosting start time calculated for another refrigerating and air-conditioning apparatus is less than or equal to a predetermined target start time interval, the defrosting operation control unit of the system controller transmits a defrosting start instruction signal to the defrosting unit of the given refrigerating and air-conditioning apparatus.

Advantageous Effects of Invention

In the refrigerating and air-conditioning apparatus according to the embodiment of the present invention, in the case where each of the time intervals between the defrosting start times between the refrigerating and air-conditioning apparatuses is less than or equal to the predetermined target start time interval, one of the refrigerating and air-conditioning apparatuses is instructed to start the defrosting operation even if it does not satisfy a defrosting start condition. It is therefore possible to minimize the possibility that some of the plurality of refrigerating and air-conditioning apparatuses will simultaneously start the defrosting operation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a control system of the entire refrigerating and air-conditioning system according to embodiment 1 of the present invention.

FIG. 2 is a schematic block diagram illustrating each of refrigerating and air-conditioning apparatuses included in the refrigerating and air-conditioning system according to embodiment 1.

FIG. 3 is a schematic block diagram illustrating a system controller in the refrigerating and air-conditioning system according to embodiment 1.

FIG. 4 is a flowchart illustrating an immediate defrosting start-instruction issuing operation by the refrigerating and air-conditioning system according to embodiment 1.

FIG. 5 is a flowchart illustrating a defrosting start instruction issuing operation by a refrigerating and air-conditioning system according to embodiment 2 of the present invention.

FIG. 6 is a diagram illustrating an example of selection of any of operation patterns in the refrigerating and air-conditioning system according to embodiment 2.

FIG. 7 is a flowchart illustrating an operation to determine whether or not an energy-saving operation can be performed in a refrigerating and air-conditioning system according to embodiment 3 of the present invention.

FIG. 8 is a diagram illustrating an example of selection of any of operation patterns and selection of any of groups for the energy-saving operation in the refrigerating and air-conditioning system according to embodiment 3.

DESCRIPTION OF EMBODIMENTS Embodiment 1

Embodiment 1 relates to a refrigerating and air-conditioning system according to the present invention which is applied to a low-temperature warehouse for business use.

FIG. 1 is a schematic diagram illustrating a control system of the entire refrigerating and air-conditioning system according to embodiment 1 of the present invention. FIG. 2 is a schematic block diagram illustrating each of refrigerating and air-conditioning apparatuses in the refrigerating and air-conditioning system. FIG. 3 is a schematic block diagram illustrating a system controller in the refrigerating and air-conditioning system.

Referring to FIG. 1, the refrigerating and air-conditioning system according to embodiment 1 includes four refrigerating and air-conditioning apparatuses G1 to G4 and a system controller 100 which is connected to controllers b1 to b4 of the refrigerating and air-conditioning apparatuses G1 to G4 by communication lines 11 such that they can perform two-way communications with the controllers, and which manages operations of the refrigerating and air-conditioning apparatuses G1 to G4 in an integrative manner. The refrigerating and air-conditioning apparatuses G1 to G4 includes evaporators which are provided in a target space 10 to be cooled. The above system controller 100 manages the entire system in an integrative manner, while performing two-way communications with the controllers b1 to b4 of the refrigerating and air-conditioning apparatuses G1 to G4.

The above refrigerating and air-conditioning apparatuses G1 to G4 are provided independently of each other. As illustrated in FIG. 2, the refrigerating and air-conditioning apparatuses G1 to G4 include heat source units c1 to c4, unit coolers al to a4 and the controllers b1 to b4, respectively. The heat source units c1 to c4 each include a compressor 21, a condenser 22 and an accumulator 25. The unit coolers al to a4 each include an expansion valve 23 and an evaporator 24. The controllers b1 to b4 each include an operation control unit 34 which controls an operation of an associated one of the refrigerating and air-conditioning apparatuses G1 to G4. In each of the heat source units c1 to c4 and an associated one of the unit coolers al to a4, the compressor 21, the condenser 22, the expansion valve 23 and the evaporator 24 are connected by refrigerant pipes 28, whereby a refrigerant circuit 32 is formed. In the refrigerant circuit 32, in the condenser 22, heat exchange is performed between refrigerant and air sent from a fan 30, and in the evaporator 24, heat exchange is performed between the refrigerant and air sent from a fan 31. Each of the refrigerating and air-conditioning apparatuses G1 to G4 further includes an operation-state detecting unit 35 which detects an operation state of the refrigerant circuit 32, a frost detection unit SA which detects frost adhering on a surface of a refrigerant tube for the evaporator 24, and a defrosting unit 33 which removes the frost on the evaporator 24. The frost detection unit SA includes, for example, an infrared sensor, etc. The defrosting unit 33 includes, for example, a bypass pipe 29, a solenoid opening/closing valve 27 and a solenoid opening/closing valve 26. The bypass pipe 29 is connected as a bypass from a point between the compressor 21 and the condenser 22 in the refrigerant circuit 32 to a point between the expansion valve 23 and the evaporator 24. The solenoid opening/closing valve 27 is provided at part of the bypass pipe 29. The solenoid opening/closing valve 26 is provided downstream of the condenser 22 in a flow direction of the refrigerant in the refrigerant circuit 32. A normal cooling operation of the refrigerant circuit 32 is performed, with the solenoid opening/closing valve 26 opened, and the solenoid opening/closing valve 27 fully closed. By contrast, a defrosting operation is performed, with the solenoid opening/closing valve 26 fully closed and the solenoid opening/closing valve 27 opened.

Each of the controllers b1 to b4 includes, for example, a microcomputer, and has functions of the operation control unit 34 which controls the operation of the refrigerant circuit 32. The operation-state detection unit 35 includes an evaporator-inlet refrigerant temperature detecting unit MI which detects the temperature of the refrigerant at a refrigerant inlet of the evaporator 24, an evaporator-outlet refrigerant temperature detecting unit MD which detects the temperature of the refrigerant at a refrigerant outlet of the evaporator 24, an evaporator-inlet air temperature detecting unit MAI which detects the temperature of air on an air-inlet side of the evaporator 24, an evaporator-outlet air temperature detecting unit MAD which detects the temperature of air on an air-outlet side of the evaporator 24, a low-pressure-side pressure detecting unit LP which detects a pressure on a downstream side of the evaporator 24 in the refrigerant circuit 32, a fan rotation-speed detecting unit RA which detects a rotation speed of the fan 31 which sends air to the evaporator 24, and the frost detection unit SA. Detected values of those units are input to a data input unit included in the above each of the controllers b1 to b4. The controllers b1 to b4 each include a data output unit, from which driving instruction signals are output to an inverter motor MV which drives the compressor 21 and valve driving units for the expansion valve 23 and the solenoid opening/closing valves 26 and 27, to thereby perform the cooling operation or the defrosting operation.

As illustrated in FIG. 3, the system controller 100 includes a central processing unit (CPU) 40 as a main element, and further includes a nonvolatile memory ME, a timing unit C such as a clock or a timer, which measures time taken by processing, etc., and a data bus DB including input/output ports. To an input side of the data bus DB, communication lines 11 for receiving signals from the controllers b1 to b4 of the refrigerating and air-conditioning apparatuses G1 to G4 and a remote control unit 36 which receives setting data from an external device are connected. To an output side of the data bus DB, communication lines 11 for outputting control instruction signals to the controllers b1 to b4 of the refrigerating and air-conditioning apparatuses G1 to G4 are connected.

The CPU 40 has as program software, various functions of an unified management unit 41, an estimated defrosting start-time calculating unit 42, a defrosting operation control unit 43, an accumulated cooling operation calculating unit 44 and a cooling-operation availability calculating unit 45, which will be described in detail later. Those functions are stored as program data in the memory ME, and are read from the memory ME as occasion arises, and used in the CPU 40. In addition, for example, data regarding the refrigerating and air-conditioning apparatuses G1 to G4, set target data (representing, for example, 1 degree C., 2 degrees C., and 3 degrees C.) regarding the difference between refrigerant temperatures at the inlet and the outlet of the evaporator 24, set target time data (representing, for example, 1 minute and 30 minutes), which are set and input using the remote control unit 36, are stored in the memory ME in advance. Additionally, for example, various operation-state data items obtained through detection by the above detecting units, historical data related to those data items, sorted data items regarding calculated estimated defrosting start times, and data regarding a target ratio of a system capacity to a required capacity are sequentially stored in the memory ME and are used.

An operation will now be described. An immediate defrosting start-instruction issuing operation of the refrigerating and air-conditioning system having the above configuration will be described. Each of the controllers b1 to b4 of the refrigerating and air-conditioning apparatuses G1 to G4 holds in its memory an initial value X of an operation time period which is set as time for which the operation will be performed until the start of subsequent defrosting. It is determined that a defrosting start condition is satisfied when either of the following conditions is satisfied: when an accumulated cooling-operation duration exceeds the initial value X; and when the degree of superheat of the refrigerant at the outlet of the evaporator 24 falls below a predetermined target value. Whether the former condition is satisfied or not is determined from the initial value X and a cooling operation availability of the apparatus, which is found based on the time interval from a thermo-off state to a thereto-on state. Whether the latter condition is satisfied or not is determined by carrying out the following steps: estimating the degree of superheat of the refrigerant (=the refrigerant temperature at the outlet of the evaporator 24—the refrigerant temperature at the inlet of the evaporator 24) at the outlet of the evaporator 24, which is obtained after a lapse of predetermined time on the basis of a change of the refrigerant temperature at the inlet of the evaporator 24 which is made with the passage of time and a change of the refrigerant temperature at the outlet of the evaporator 24 which is made with the passage of time, in consideration of a fact that as the amount of frost on the evaporator 24 increases, the efficiency of heat exchange in the evaporator 24 decreases, and refrigerant will not easily evaporate; calculating an estimated time at which the amount of frost will reach a defrosting-start reference value stored in the memory ME, thereby determining a subsequent estimated defrosting start time; and periodically transmitting information regarding the estimated defrosting start time to the system controller 100 including the unified management unit 41. This calculation may be performed by the CPU 40 of the system controller 100. If so, the estimated defrosting start-time calculating unit 42 in the CPU 40 calculates estimated defrosting start times for the refrigerating and air-conditioning apparatuses G1 to G4, at which the defrosting operations of the respective defrosting units 33 will be started, based on the operation states of the refrigerating and air-conditioning apparatuses G1 to G4 which are detected by the respective operation-state detection units 35.

As illustrated in the flowchart of FIG. 4, the CPU 40 of the system controller 100 sorts the estimated defrosting start times transmitted from the refrigerating and air-conditioning apparatuses G1 to G4, on the time series in the order from the estimated defrosting start time closest to the present time, to thereby determine the sorted times as estimated defrosting start times Ti, . . . and Tn (n=4 in this example), and temporarily stores data indicating these times in the memory ME (step S1). Then, the estimated defrosting start time T1 for a refrigerating and air-conditioning apparatus, which is the closest to the present time, is set as time to be referred to in the following determination (step S2). In step S3, it is determined whether or not a time interval (T(i+1)−Ti) between the closest estimated defrosting start time Ti (i=1 at the beginning) and the second closest estimated defrosting start time T(i+1) exceeds a target start time interval (30 minutes in this example) stored in the memory ME. If the time interval exceeds the target start time interval (No in step S3), the process proceeds to step S4 and then to step S5. Steps S3 to S5 are repeated for all of the refrigerating and air-conditioning apparatuses G1 to G4. By contrast, in step S3, if the calculated time interval is less than or equal to the target start time interval (Yes), the defrosting operation control unit 43 of the system controller 100 transmits a defrosting start instruction signal to the controller of a refrigerating and air-conditioning apparatus for which the closest estimated defrosting start time Ti is calculated (step S6). In response to the defrosting start instruction signal, the controller of the refrigerating and air-conditioning apparatus drives the defrosting unit 33 to perform the defrosting operation on the evaporator 24.

Specifically, in the case where the time interval between an estimated defrosting start time calculated for a certain refrigerating and air-conditioning apparatus and the subsequent estimated defrosting start time calculated for another refrigerating and air-conditioning apparatus is less than or equal to a predetermined target start time interval (for example, 30 minutes), the defrosting operation control unit 43 of the system controller 100 transmits a defrosting start instruction signal to the defrosting unit 35 of the above certain refrigerating and air-conditioning apparatus. The defrosting operation control unit 43 controls the defrosting operation of the defrosting unit 35 on the basis of the estimated defrosting start time calculated by the estimated defrosting start-time calculating unit 42.

That is, the system controller 100 monitors whether or not each of the differences Ti between the estimated defrosting start times for the refrigerating and air-conditioning apparatuses G1 to G4 falls below a time period Y required for the defrosting operation of each apparatus. If any of the differences Ti satisfies Ti<Y, the system controller 100 gives a defrosting start instruction to a refrigerating and air-conditioning apparatus the estimated defrosting start time of which is the earliest, for example, the refrigerating and air-conditioning apparatus G1. After the defrosting operation of the refrigerating and air-conditioning apparatus G1 ends, the system controller 100 re-determines whether any of the differences satisfies Ti<Y. Also, if any of the differences Ti satisfies Ti<Y, the system controller 100 gives a defrosting start instruction to the refrigerating and air-conditioning apparatus G3 the estimated defrosting start time of which is the second earliest. The above control is repeated. If some of the refrigerating and air-conditioning apparatuses satisfy the defrosting start condition, each of those refrigerating and air-conditioning apparatuses is caused to start the defrosting operation.

As described above, according to embodiment 1, in the case where each of the time intervals between the estimated defrosting start times of the refrigerating and air-conditioning apparatuses G1 to G4 is less than the time required for defrosting, an instruction to start the defrosting operation is issued even if the start condition is not satisfied. It is therefore possible to minimize the possibility that some of the refrigerating and air-conditioning apparatuses will simultaneously start the defrosting operation.

Furthermore, each of the refrigerating and air-conditioning apparatuses G1 to G4 is allowed to start the defrosting operation before the amount of frost on the apparatus exceeds an assumed amount of frost. Therefore, it is possible to prevent liquid backflow to the compressor 21 which would be caused by an excessive amount of frost, and further achieve energy saving since the time required for defrosting is shortened.

In addition, the interval between defrosting operations is closer to an optimum interval than in a schedule method in which a defrosting start time is specified. It is therefore possible to improve the energy saving of the entire cycle in which cooling and defrosting are repeated.

In embodiment 1, the accumulated cooling-operation duration and the degree of superheat of the refrigerant at the outlet of the evaporator are used in order for the estimated defrosting start-time calculating unit 42 to calculate and estimate an estimated defrosting start time. In addition, it is also possible to apply to the operation of the estimated defrosting start-time calculating unit, the following methods: for example, a method of detecting formation of frost using a frost detecting device which includes a light-emitting element including a light-emitting diode (LED) and a light-receiving element including an LED as described in Japanese Patent No. 4767053; a method of detecting reduction of the rotation speed RA of the fan 31, which is caused by an increase in the static pressure in the unit cooler caused by frost; and a method of digitizing a change in heat exchange efficiency, which is made by formation of defrost, this digitization being achieved by observing for a given time, the difference between the temperature of air on the suction side of the evaporator 24 which is detected by the evaporator-inlet air temperature detecting unit MAI and the temperature of air on the discharge side of the evaporator 24 which is detected by the evaporator-outlet air temperature detecting unit MAD, and the temperature of the refrigerant at the inlet of the evaporator 24. Furthermore, such methods using different detection parameters as described above can be used in combination to estimate a defrosting start time accurately for further various environmental conditions and applications.

The detection accuracy of an estimating unit is reduced under a given installation environment or application. For example, in the case where the target space 10 to be cooled is used to store items to be frequently replaced by other or new items, outdoor air enters the target space 10, causing fluctuations in the temperature of air on the inlet side of the evaporator 24. In this case, it suffices that the controllers b1 to b4 are made to have a function of selecting which estimating unit should be used. If so, the accuracy of estimation of a defrosting start time can be improved.

Embodiment 2

Embodiment 2 relates to an improvement of the control described with respect to embodiment 1. To be more specific, in embodiment 2, the refrigerating and air-conditioning apparatuses G1 to G4 are allowed to perform defrosting to the extent to which the required cooling capacity is not affected.

Embodiment 2 also relates to a similar control to that in the refrigerating and air-conditioning system as illustrated in FIG. 1. FIG. 5 is a flowchart of the process of determining whether to issue a defrosting start instruction, in embodiment 2 of the present invention. FIG. 6 illustrates a concrete example of operation pattern selection in embodiment 2.

An operation will now be described.

In the refrigerating and air-conditioning system configured in the above manner, the system controller 100 arranges estimated defrosting start times transmitted from the refrigerating and air-conditioning apparatuses G1 to G4 on the time series, and monitors whether each of the differences Ti between the defrosting start times for the refrigerating and air-conditioning apparatuses G1 to G4 is less than the time period Y (30 minutes in the example as indicated in FIG. 5) required for the defrosting operation of each apparatus. On these points, embodiment 2 is the same as embodiment 1. Furthermore, in embodiment 2, the system controller 100 performs the following control in order to determine whether some of the refrigerating and air-conditioning apparatuses are simultaneously allowed to perform defrosting.

The flowchart of FIG. 5 illustrates a concrete example of the control. Steps S1 to S5 in the flowchart of FIG. 5 are the same as those illustrated in the flowchart of FIG. 4 in embodiment 1, and their descriptions will thus be omitted. In step S3, if the calculated time interval is less than or equal to the target start time interval (Yes), the defrosting operation control unit 43 of the system controller 100 sets as 1, the number j of groups (variable j in the example of FIG. 5) to start defrosting operation simultaneously (step S7). Subsequently, the defrosting operation control unit 43 of the system controller 100 calculates each of system cooling capacities Qj of the refrigerating and air-conditioning system in the case where 1 to j groups simultaneously perform defrosting operation, on the basis of a cooling capacity required for the target space 10 to be cooled (refrigerator), a cooling capacity of each refrigerant system group, and the amount of heat generated at the unit-cooler in the defrosting operation of each refrigerant system group (step S8). This process, as described later, is performed successively on all refrigerating and air-conditioning apparatuses which are scheduled to start defrosting before defrosting of the refrigerating and air-conditioning apparatuses of group 1 ends (within 39 minutes of starting of the defrosting operation in embodiment 2). Then, in step S9, it is determined whether the calculated system cooling capacity Qj is less than the required capacity or not. In step S9, if the system cooling capacity Qj is less than the required capacity (Yes), the number k of groups is set to 2 (k=2) in step S10, and the process proceeds to the process of step S11. In step S9, if the system cooling capacity Qj is larger than or equal to the required capacity (No), it is determined in step S12 whether the time interval (Tj−Ti) between the closest estimated defrosting start time Ti and a defrosting start time Tj, at which the defrosting operation can be simultaneously started, is longer than the target start time interval (30 minutes) or not. In step S12 if the time interval is less than or equal to the target start time interval (No), the number j of groups to start the defrosting operation simultaneously is increased by one (step S13), and the process returns to step S8. Steps S8, S9, S12, and S13 are repeated for all of the refrigerating and air-conditioning apparatuses G1 to G4.

By contrast, in step S2, if the time interval is longer than the target start time interval (Yes), the process proceeds to step S10 and then to step S11. In step S11, a system cooling capacity Qk in the defrosting operation of 2 to k groups is calculated, and the process proceeds to step S14. In step S14, it is determined whether the calculated system cooling capacity Qk is less than the required capacity. In step S14, if the system cooling capacity Qk is less than the required capacity (Yes), a proper operation pattern (see FIG. 6, which will be referred to later) is selected in step S15. A defrosting start instruction signal is transmitted to each of the controllers of the refrigerating and air-conditioning apparatuses that are determined to start defrosting (step S16). In step S14, if the system cooling capacity Qk is larger than or equal to the required capacity (No), steps S18, S11, S14, and S17 are repeated until k becomes equal to j.

To be more specific, on the basis of the cooling capacity required for the inside of the refrigerator, a cooling capacity of each refrigerating and air-conditioning apparatus, and the amount of heat generated at the unit-cooler in the defrosting operation of each refrigerating and air-conditioning apparatus, the number of groups (variable j in the example of FIG. 5) to start defrosting operation simultaneously with a group to start defrosting operation before ending of the defrosting operation of the refrigerating and air-conditioning apparatus of a first group (within 30 minutes of starting of the defrosting operation in embodiment 2) is incremented by one and this increment is repeated until the system cooling capacity Qj falls below the required capacity, that is, “Qj<required capacity”.

FIG. 6 illustrates selection of any of multi-apparatus simultaneous defrosting patterns. Referring to FIG. 6, the following system capacities are calculated: a system capacity (the system capacity=the sum of cooling capacities of groups performing the cooling operation−the sum of the amounts of heat generated in groups performing the defrosting operation) to be obtained in the case where group 4 and group 3 start the defrosting operation simultaneously with group 1; a system capacity to be obtained in the case where only group 1 starts defrosting operation, and then only group 4 starts the defrosting operation; and a system capacity to be obtained in the case where only group 1 starts the defrosting operation, and then group 4 and group 3 starts the defrosting operation. Then, with respect to the operation patterns, patterns (patterns 1 and 2) in which the required capacity (20 KW in embodiment 2) is ensured are stored as selectable operation patterns.

Then, in the case where two groups need to perform the defrosting operation simultaneously, system capacities Qk are calculated as information for use in determining whether to cause the two groups to perform the defrosting simultaneously in a first defrosting operation or in a second defrosting operation. In the example as illustrated in FIG. 6, in the case where the system capacities Qk are calculated with respect to pattern 4 in which only group 4 performs the defrosting operation and pattern 5 in which group 4 and group 3 automatically perform the defrosting operation, the required capacity, 20 kW, is ensured only in pattern 4. Therefore, when this result is added to the result of the above calculation, it is found that selectable operation patterns are patterns 1, 2 and 4, that is, any of these patterns is selected.

After the system capacities in the operation patterns are calculated, the process proceeds to the step of selecting any of the operation patterns. In this example, the required capacity is ensured in pattern 1, pattern 2, and pattern 4. However, because the current time is 10:00 and defrosting by each group takes 30 minutes, it is impossible for groups 1 to 4 to complete defrosting in this order by 10:35 which is the defrosting start time for group 3, which will perform defrosting third, Consequently, pattern 4 cannot be selected.

Also, even if pattern 1 is selected, group 4 will start defrosting at 10:30, and group 3 will start defrosting at 10:35. This will be practically equivalent to selection of pattern 5, in which the system capacity will become insufficient. Accordingly, pattern 1 cannot also be selected. Therefore, in this example, pattern 2 is selected, and a defrosting start instruction is issued to each of group 1 and group 4.

As described above, according to embodiment 2, a plurality of refrigerating and air-conditioning apparatuses are simultaneously allowed to perform the defrosting operation to the extent to which the required system capacity is ensured. Even if the defrosting operation of each of three or more refrigerating and air-conditioning apparatuses is scheduled within a short time period, it is possible to operate the system without causing the system capacity to be insufficient.

Furthermore, the above determination is also considered for the case where a given refrigerating and air-conditioning apparatus first performs the defrosting operation, and then another or other refrigerating and air-conditioning apparatuses perform the defrosting operation, as a result of which such a plurality of refrigerating and air-conditioning apparatuses perform the defrosting operation. Therefore, it is possible to prevent the system capacity from being insufficient after only the above given refrigerating and air-conditioning apparatus first performs the defrosting operation, as described above with respect to embodiment 2.

In embodiment 2, all refrigerating and air-conditioning apparatuses belonging to a single group are targets to be selected in operation pattern selection. In the case where a single group consists of many refrigerating and air-conditioning apparatuses, logic for operation pattern selection is complicated, as a result of which the performance of the system controller 100 may be reduced. Therefore, in the case where the accuracy of estimation of an estimated defrosting start time for a refrigerating and air-conditioning apparatus is low, for example, in the case where the time interval between the present time and the estimated defrosting start time for the refrigerating and air-conditioning apparatus is three hours or more, the refrigerating and air-conditioning apparatus can be removed from targets to be selected, thus reducing a calculation load on the system.

Furthermore, in embodiment 2, a group which can start defrosting operation before a first refrigerating and air-conditioning apparatus ends the defrosting operation is set as a target for operation pattern selection. In the case where the number of groups which can start the defrosting operation simultaneously is limited by restrictions, such as the capacity of a circuit-breaker, the number j of apparatuses as indicated in the flowchart of FIG. 5 can be limited to the number of groups which can perform he defrosting operation simultaneously, in order to solve the problem which will arise due to the above restrictions.

Embodiment 3

According to embodiment 3, in addition to the controls described with respect to embodiments 1 and 2, a capacity-saving operation is performed in the case where the system cooling capacity is sufficient, thus also achieving energy saving in the cooling operation.

Embodiment 3 also relates to control over a refrigerating and air-conditioning system, which is similar to that over the refrigerating and air-conditioning system as illustrated in FIG. 1. It is determined whether to issue a defrosting start instruction, in the manner as indicated in the flowchart of FIG. 5 as in embodiment 2.

The operation of embodiment 3 will be described.

In the refrigerating and air-conditioning system with such a configuration, the system controller 100 performs an optimum control of the defrosting operation interval as described with respect to embodiment 2, and further determines whether the present system capacity is excessively larger than the required capacity, and perform control to stop a refrigerating and air-conditioning apparatus or apparatuses if the system capacity is excessively larger.

To be more specific, a capacity-saving operation control as indicated in the flowchart of FIG. 7 is performed concurrently with the optimum control of the defrosting operation interval as indicated in the flowchart of FIG. 5.

Referring to the flowchart of FIG. 7, the system controller 100 first determines whether the ratio of the system capacity to the required capacity exceeds 150% or not (step S21). If the capacity ratio exceeds 150% (Yes in step S21), it is determined in step S22 whether the inner temperature of the refrigerator in the target space 10 rises or not. If it does not rise (Yes in step S22), the process proceeds to step S23, In step S23, it is determined whether an operating frequency, which is a driving signal to be transmitted to the inverter motor MU for each compressor 21, continuously drops or not. If it continuously drops (Yes), a thereto-off instruction signal is transmitted to the controller of the refrigerating and air-conditioning apparatus i associated with the shortest time interval (Ti−T(i−1)) (step S24). If the operating frequency does not continuously drop (No in step S23), it is determined in step S25 whether the pressure on a low-pressure side in the refrigerant circuit 32, which is located downstream of the expansion valve 23 in the flow direction of the refrigerant, continuously drops or not. If the pressure on the low-pressure side continuously drops (Yes), the process proceeds to step S24 described above. If the pressure on the low-pressure side does not continuously drop (No), the process returns to step S22. Steps S22, S23 and S25 are repeated.

That is, according to embodiment 3, the cooling capacity required for the target space 10 is compared with the system capacity obtained based on the cooling capacities of the groups and the amounts of heat generated in the unit-coolers in the defrosting operation of the groups. If it is determined that the system capacity is sufficient, for example, the ratio of the system capacity to the required capacity is 150% or higher, the control is shifted to that of a routine of the capacity-saving operation.

To be more specific, in the routine of the capacity-saving operation, after it is confirmed that the system capacity is sufficient with respect to the cooling load in the target space 10 based on changes in parameters, such as the inner temperature of the refrigerator which is detected by each evaporator-inlet air temperature detecting unit MAI, the operating frequency for each compressor 21, and the pressure on the low-pressure side in an evaporating temperature which is detected by the low-pressure-side pressure detecting unit, a refrigerating and air-conditioning apparatus which is in cooling operation, which belongs to the group associated with the shortest time interval between the estimated defrosting start times, and which is associated with a later estimated defrosting start time, is caused to enter the thermo-off state, as illustrated in FIG. 8.

As described above, according to embodiment 3, the control for causing a refrigerating and air-conditioning apparatus or apparatuses to enter the thermo-off state in the case where the system cooling capacity is sufficient is performed, in addition to the optimum control of the defrosting operation interval, which is described with respect to embodiment 2. Thereby, it is possible to perform the operation with further energy saving, while maintaining the required cooling capacity.

In the control, it is monitored at all times whether the refrigerator temperature rises or not. Thus, when a refrigerating and air-conditioning apparatus is caused to be in the thermo-off state, even if the system capacity falls below the required capacity, the refrigerating and air-conditioning apparatus being in the thermo-off state can be caused to resume the cooling operation at a proper timing. Therefore, it is possible to achieve both management of the inner temperature of the refrigerator and the energy-saving operation.

Furthermore, one of groups associated with the shortest one of the time intervals between estimated defrosting start times of all the groups is caused to be in the thermos-off state, the estimated defrosting start time of the above one of the groups being later than that of the other, thereby increasing the shortest time interval, and thus reducing the risk that those groups may simultaneously start the defrosting operation.

As described above, the refrigerating and air-conditioning system of the present invention has the following features: in the case where the difference between the present time and the estimated defrosting start time of a refrigerating and air-conditioning apparatus is greater than or equal to a predetermined value, the refrigerating and air-conditioning apparatus is eliminated from targets to be applied to the above determination; the number of determination targets is set greater than or equal to a certain number which is determined with respect to the total number of refrigerating and air-conditioning apparatuses included in the system; the capacity-saving operation is performed in the case where the system cooling capacity is sufficient; and when the temperature of the refrigerant at the inlet of the evaporator is a certain value or higher, the defrosting operation is not performed.

The above embodiments are described above by referring to by way of example the case where the refrigerating and air-conditioning system is applied to a commercial low-temperature warehouse. The refrigerating and air-conditioning system of the present invention is also applicable to air-conditioning of a room.

REFERENCE SIGNS LIST

10 cooled space 11 communication line 21 compressor 22 condenser expansion valve 24 evaporator 25 accumulator 26 solenoid opening/closing valve 27 solenoid opening/closing valve 28 refrigerant pipe 29 bypass pipe 30 fan 31 fan 32 refrigerant circuit 33 defrosting unit 34 operation control unit 35 operation-state detection unit 40 CPU 41 unified management unit 42 estimated defrosting start-time calculating unit 43 defrosting operation control unit 44 accumulated cooling operation calculating unit 45 cooling-operation availability calculating unit 100 system controller G1, G2, G3, G4 refrigerating and air-conditioning apparatus a1, a2, a3, a4 unit cooler b1, b2, b3, b4 controller c1, c2, c3, c4 heat source unit C timing unit DB data bus LP low-pressure-side pressure detecting unit MI evaporator-inlet refrigerant temperature detecting unit MAD evaporator-outlet air temperature detecting unit MAI evaporator-inlet air temperature detecting unit MD evaporator-outlet refrigerant temperature detecting unit ME memory MV inverter motor M motor RA fan rotation-speed detecting unit SA frost detection unit 

1. A refrigerating and air-conditioning system comprising: a plurality of refrigerating and air-conditioning apparatuses provided independent of each other and each of which includes a refrigerant circuit in which a compressor, a condenser, an expansion valve and an evaporator are connected, and each of which detects an operation state of the refrigerant circuit, and removes frost forming on the evaporator; and a system controller configured to manage operations of the plurality of refrigerating and air-conditioning apparatuses in an integrative manner, the system controller being configured to: calculate an estimated defrosting start time, at which a defrosting operation to remove the frost forming on the evaporator is to be started, for each of the plurality of refrigerating and air-conditioning apparatuses, based on the operation state of the refrigerant circuit of the each of the plurality of refrigerating and air-conditioning apparatuses control the defrosting operation based on the estimated defrosting start time; and cause the defrosting operation of one of the plurality of refrigerating and air-conditioning apparatuses to start earlier than the estimated defrosting start time, in a case where a time interval between the estimated defrosting start time for the one of the plurality of refrigerating and air-conditioning apparatuses and the estimated defrosting start time for an other one of the plurality of refrigerating and air-conditioning apparatuses is less than or equal to a predetermined time interval.
 2. The refrigerating and air-conditioning system of claim 1, wherein the system controller is configured to: calculate an accumulated cooling-operation duration which is to increase until start of defrosting of the each of the plurality of refrigerating and air-conditioning apparatuses and a cooling operation availability of the each of the plurality of refrigerating and air-conditioning apparatuses; and calculate the estimated defrosting start time for the each of the plurality of refrigerating and air-conditioning apparatuses based on the accumulated cooling-operation duration and the cooling operation availability.
 3. The refrigerating and air-conditioning system of claim 1, wherein the evaporators of the plurality of refrigerating and air-conditioning apparatuses are disposed in a single target space to be cooled.
 4. The refrigerating and air-conditioning system of claim 1, wherein the plurality of refrigerating and air-conditioning apparatuses each detect frost forming on a refrigerant tube for the evaporator, and wherein the system controller is configured to calculate the estimated defrosting start time for the each of the plurality of refrigerating and air-conditioning apparatuses based on a degree of formation of the frost detected by the plurality of refrigerating and air-conditioning apparatuses.
 5. The refrigerating and air-conditioning system of claim 1, wherein the plurality of refrigerating and air-conditioning apparatuses each detect a temperature of refrigerant at an inlet of the evaporator and a temperature of the refrigerant at an outlet of the evaporator, and wherein the system controller is configured to calculate the estimated defrosting start time for the each of the plurality of refrigerating and air-conditioning apparatuses based on the temperature of the refrigerant at the inlet of the evaporator and the temperature of the refrigerant at the outlet of the evaporator, which are both detected by the plurality of refrigerating and air-conditioning apparatuses.
 6. The refrigerating and air-conditioning system of claim 1, wherein the plurality of refrigerating and air-conditioning apparatuses each detect a rotation speed of a fan configured to send air to the evaporator, and wherein the system controller is configured to calculate the estimated defrosting start point for the each of the plurality of refrigerating and air-conditioning apparatuses based on a change of the rotation speed of the fan which is made with passage of time, the rotation speed of the fan being detected by the plurality of refrigerating and air-conditioning apparatuses.
 7. The refrigerating and air-conditioning system of claim 1, wherein plurality of refrigerating and air-conditioning apparatuses each detect a temperature of refrigerant at an inlet of the evaporator, a temperature of air on a suction side of the evaporator, and the temperature of the air on a discharge side of the evaporator, and wherein the system controller is configured to calculate the estimated defrosting start time for the each of the plurality of refrigerating and air-conditioning apparatuses based on a change of the temperature of the refrigerant at the inlet of the evaporator which is made with passage of time, a change of the temperature of the air on the suction side of the evaporator which is made with passage of time, and a change of the temperature of the air on the discharge side of the evaporator which is made with passage of time, the temperature of the refrigerant at the inlet of the evaporator, the temperature of the air on the suction side of the evaporator and the temperature of the air on the discharge side of the evaporator being all detected by the plurality of refrigerating and air-conditioning apparatuses.
 8. The refrigerating and air-conditioning system of claim 1, wherein with respect to ones of the plurality of refrigerating and air-conditioning apparatuses, for which at least one interval between estimated defrosting start times of the ones of the plurality of refrigerating and air-conditioning apparatuses is shorter than or equal to a predetermined time interval, the system controller prepares operation patterns in each of which the ones of the plurality of refrigerating and air-conditioning apparatuses are arbitrarily combined to simultaneously perform defrosting operation, and selects one of the operation patterns based on a system capacity of the refrigerating and air-conditioning apparatus at time of applying each of the operation patterns and a cooling capacity required for the plurality of refrigerating and air-conditioning apparatuses.
 9. A system controller configured to manage in an integrative manner a plurality of refrigerating and air-conditioning apparatuses provided independent of each other and each of which includes a refrigerant circuit in which a compressor, a condenser, an expansion valve and an evaporator are connected, and each of which detects an operation state of the refrigerant circuit, and removes frost formed on the evaporator, the system controller being configured to: calculate an estimated defrosting start time, at which a defrosting operation to remove the frost formed on the evaporator is to be started, for each of the plurality of refrigerating and air-conditioning apparatuses, based on the operation state of the refrigerant circuit of the each of the plurality of refrigerating and air-conditioning apparatuses, and control the defrosting operation based on the estimated defrosting start time; and cause the defrosting operation of one of the plurality of refrigerating and air-conditioning apparatuses to start earlier than the estimated defrosting start time, in a case where a time interval between the estimated defrosting start time for the one of the plurality of refrigerating and air-conditioning apparatuses and the estimated defrosting start time for an other one of the plurality of refrigerating and air-conditioning apparatuses is less than or equal to a predetermined time interval. 